The present invention relates to a gas bag or so-called air bag arrangement, and includes a gas generator that serves for generating gas and an air bag that is connected to the gas generator. The gas generator has a combustion chamber for receiving the propellant, with discharge openings being disposed in the wall of the combustion chamber, and at least one filter being provided that follows the combustion chamber such that, while forming a cooling zone, the generated gas flows out of the combustion chamber and via the filter into the air bag.
During the burning or combustion of propellants for the generation of the gas required for inflating the air bag, there exists the problem that the thereby resulting impurities attack the fabric of the air bag and to this extent can adversely affect the function of the air bag arrangement. In this connection, the occurrence of impurities is essentially a function of the chemical composition of the propellant that is used.
Several main groups of propellants are used. For example, a first group includes sodium azide propellants which at a combustion temperature of about 1400.degree. C. produce only solid impurities that can be easily filtered out of the gas stream with a simple filter arrangement.
Included in a second group are nitro cellulose propellants that at a combustion temperature of about 2600.degree. C. produce gasses that are nearly free of impurities and that thus require no mechanical filtration.
The subject matter of the present application is a third group of composite propellants that due to their chemical composition and the high combustion temperature of about 2500.degree. C. produce liquid and gaseous particles as impurities that, due to the high flow velocities that result during the combustion, cannot at all or only to a very limited extent be mechanically filtered.
An air bag arrangement having the features initially mentioned is disclosed in U.S. Pat. No. 5,505,488. The gas generator of this arrangement has a first and a second filter element that each surround the wall of the combustion chamber in an annular fashion and are not spaced therefrom, and furthermore are intended to filter solid particles contained in the generated gas stream. Unfortunately, such a filter unit that directly adjoins the wall of the combustion chamber is not suitable for separating out impurities that are present in a liquid or gaseous phase from a gas stream generated by a composite propellant.
It is therefore an object of the present invention, for a gas generator operated with a composite propellant, to provide a filter unit by means of which liquid and/or gaseous impurities that result during combustion can be separated out.